Thermoplastic pipes, fittings and valves have received wide commercial acceptance in both industrial and residential markets in view of their relatively light weight, their relatively low cost and installation efficiencies as compared to most metallic pipes, fittings and valves. Furthermore, the thermoplastic materials from which these pipes, fittings and valves can be made are particularly resistant to caustic chemicals. As a result, thermoplastic pipes, fittings and valves have been widely accepted by the chemical and petrochemical industries for transporting highly caustic chemicals.
Leaks of chemicals from pipe systems have the potential for creating catastrophic environmental damage and personal injury. In view of these risks, a substantial demand has developed recently for double-containment pipe systems. One extremely effective double-containment pipe system is shown in U.S. Pat. No. 4,786,088 which issued to Christopher G. Ziu on Nov. 22, 1988 and which is assigned to the assignee of the subject invention. The disclosure of U.S. Pat. No. 4,786,088 is incorporated herein by reference. U.S. Pat. No. 4,786,088 shows a double-containment thermoplastic pipe assembly which includes inner and outer pipes that are retained in generally concentric relationship by a plurality of resilient support clips disposed therebetween. In particular, the support clips of U.S. Pat. No. 4,786,088 comprise a resilient mounting portion which defines a cylindrical arc of approximately 270.degree.. Three support legs are fused to the mounting portion and extend generally radially therefrom. Each support leg is of generally rectangular configuration and defines a radial dimension to enable the concentric support of the inner and outer pipes relative to one another. The double-containment thermoplastic pipe assembly shown in U.S. Pat. No. 4,786,088 further includes restraint couplings having a cylindrical inner carrier pipe portion, a cylindrical outer containment pipe portion and a unitary connecting portion extending therebetween. The restraint couplings are deployed at spaced apart locations along the double-containment thermoplastic pipe system to control and isolate differential expansion that may exist between the inner and outer pipes.
The double-containment thermoplastic pipe system shown in U.S. Pat. No. 4,786,088 is assembled by sliding the support clips longitudinally along the inner carrier pipe or snapping the support clips over the inner pipe at selected spaced apart locations therealong. The inner pipe with the support clips mounted thereto is then slid longitudinally within a selected outer containment pipe. The ends of the respective inner carrier pipe and outer containment pipe of the system shown in U.S. Pat. No. 4,786,088 generally are offset relative to one another to facilitate the connection of adjacent inner containment pipes to one another and the subsequent connection of adjacent outer containment pipes to one another. In particular, the inner carrier pipe of a previously positioned portion of a system may extend a greater axial distance than the corresponding outer containment pipe. The next sequential inner carrier pipe may then be butt-fused to the previously implaced inner carrier pipe. The next outer containment pipe may then be slid axially relative to the fused inner carrier pipes to enable the butt-fusing of the outer containment pipes. As shown in U.S. Pat. No. 4,786,088, the restraint couplings have a similar offset of the inner carrier portions and outer containment portions to facilitate this sequential butt-fusion.
Although the pipe system shown in U.S. Pat. No. 4,786,088 is extremely effective, it is desirable to provide a double-containment thermoplastic pipe assembly providing even greater efficiency and effectiveness.
In view of the above, it is an object of the subject invention to provide a double-containment thermoplastic pipe assembly having support clips that more securely engage the inner carrier pipe.
It is another object of the subject invention to provide a double-containment thermoplastic pipe assembly having support clips that will not break or permanently deform when being snapped over the inner carrier pipe.
It is another object of the subject invention to provide a double-containment thermoplastic pipe assembly that facilitates the slidable axial insertion of an inner carrier pipe into an outer containment pipe.
Still another object of the subject invention is to provide a double-containment thermoplastic pipe assembly having a plurality of inexpensive supports that facilitate the simultaneous butt-fusion of both the inner carrier pipe and the outer containment pipe to adjacent inner and outer pipes.
Yet another object of the subject invention is to provide a double-containment thermoplastic pipe assembly wherein at least selected supports between the inner and outer pipes contribute to the restraint of differential expansion.